Chevrolet Repair: lifter noise, noise question, chevy van

Question
QUESTION: I have a 1999 chevy van with a 350 and less than 40,000 miles. I have run Mobil 1 from my first oil change and change it every 3000 miles. If I leave it set for a couple days the lifters clatter. It last for about 5 minutes and then quites down. I noticed that if I change oil and filter it is fine but within a month it will do the same thing. Any idea on how to keep this from happening?

ANSWER: you very likely have coolant going into the oil from your intake gaskets. Very small amounts can get into a lifter and cause it to bleed down and clatter.

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QUESTION: wouldn't it show up as white creamy stuff on the dipstick?

Answer
The orange coolant, dex cool, doesn't show up as easily as green coolant.  If a very small leak you will not see milky oil.  You will (if you can reach it) see a little slime on the pcv valve or on the oil fill cap. If you have had to add coolant I would bet that the intake gaskets are your problem. Very common and have seen many similar complaints like that.